How do ground-based sun photometers and sky imagers use angular scattering patterns and polarization to distinguish between the optical signatures of smoke aerosols and thin cloud droplets?

The records show that sky polarization patterns can carry some information about whether aerosols absorb or scatter light. For fine-mode aerosols, however, the pattern is not sensitive to absorption, so absorption is hard to detect from polarization alone ¹. For coarse-mode aerosols, the drop in downward degree of linear polarization as particles shift from scattering to absorbing slows as aerosol optical depth rises ². The available facts do not address thin cloud droplets or sun photometer methods, so they cannot show how the instruments separate smoke from thin cloud ¹². The newest fact dates from 2020, about six years before the current date of October 2026 ².

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